The present invention relates to a method for volume-selective nuclear magnetic resonance (NMR)-spectroscopy or NMR-imaging, wherein a radio frequency (RF)-pulse is irradiated onto a sample located inside a measuring volume in a homogeneous static magnetic field B.sub.o within a time interval during which an additional magnetic field gradient is applied to the measuring volume.
Such a method has been known for example from the LOSY-method published by E. Rommel and R. Kimmich in J. Magn. Reson. 83, 1989, p. 299 ff [0].
In the following, reference is made to publications cited in the reference list at the end of the specification using reference numerals in square brackets.
In the last few years several attempts have been undertaken to develop operational NMR imaging procedures for solid objects. This implies line-narrowing methods, i.e. magic-angle spinning [1] or multipulse sequences [2] , and solid-echo phase-encoding methods [3-5]. It has also been suggested that one should transfer the polarization from abundant protons to rare nuclei such as .sup.13 C in order to avoid the strong homonuclear line broadening of protons [6,7].
The latter approach in principle gives access to the spectral information of .sup.13 C NMR parameters e.g. the chemical shift anisotropy. This is a crucial requirement for potential applications in material science. One is interested in not only a good reproduction of the morphology of the object, but rather would also like to measure physical and chemical parameters characterising the local material properties [3,6]. An example is the local polymer chain orientation in plastic materials which affects spectral properties due to anisotropic spin interactions [3].
Obtaining images which directly render the spatial distribution of such spectral parameters may be an excessively time-consuming process. Image-guided localized spectroscopy therefore is expected to be a more favourable procedure for this purpose. Local solid state spectra using the localized spectroscopy (LOSY) technique [8,9] have been already studied.
In extension to this homonuclear method, heteronuclear techniques based on a new spatial selection mechanism taking place with solid-state polarization transfer methods in the presence of magnetic field gradients are described. (The term "cross-polarization" is also widespread in this context. The more general term "spin-order transfer" would be more appropriate but has not yet come into use.) The spin species predominantly referred to are heteronuclear spins 1/2, e.g. a transfer from protons to .sup.13 C nuclei. In principle spin order transfer to spins with higher quantum numbers is also feasible provided that dipolar coupling mediates the polarization transfer process.